1. Field of the Invention
The present invention relates to a sputtering target for making an optical medium such as an optical disc, a method of making the same, an optical medium, and a method of making the same.
2. Related Background Art
Optical media such as optical discs (e.g., BD (Blu-ray Disc)-R, BD-RE, and BD-ROM) and optical cards which are made by forming a reflective layer on a substrate by sputtering with a sputtering target and further forming an optical recording layer, a transparent cover layer for transmitting light therethrough at the time of reading or writing, or the like on the reflective layer have been known. Unless the reflective layer has a high surface smoothness on its film-deposition end surface side, such optical media fail to attain favorable reflection upon irradiation with laser beams, adversely affect structures of the optical recording layer, transparent cover layer, and the like formed on the reflective layer, and deteriorate characteristics such as jitter characteristics, for example.
As sputtering targets which can make reflective layers for optical media, Japanese Patent Application Laid-Open No. 2002-015464 and Japanese Translated International Patent Application Laid-Open No. 2002-518596 disclose alloys mainly composed of Ag.